An ion source is a device that causes gas molecules to be ionized and then accelerates and emits the ionized gas molecules and/or atoms in a beam towards a substrate. Such an ion beam may be used for various purposes, including but not limited to cleaning a substrate, activation, polishing, etching, and/or deposition of thin-film coatings/layer(s). Example ion sources are disclosed, for example, in U.S. Pat. Nos. 7,030,390; 6,988,463; 6,987,364; 6,815,690; 6,812,648; and 6,359,388; the disclosures of which are all hereby incorporated herein by reference.
FIGS. 1-2 illustrate a conventional cold-cathode closed drift type ion source. In particular, FIG. 1 is a side cross-sectional view of an ion beam source with an ion beam emitting slit defined in the cathode, and FIG. 2 is a corresponding sectional plan view along section line II-II of FIG. 1. FIG. 3 is a sectional plan view similar to FIG. 2, for purposes of illustrating that the FIG. 1 ion beam source may have an oval and/or racetrack-shaped ion beam emitting slit as opposed to a circular ion beam emitting slit. Any other suitable shape also may be used.
Referring to FIGS. 1-3, the ion source includes a hollow housing made of a magnetoconductive material such as steel, which is used as a cathode 5. Cathode 5 includes cylindrical or oval side wall 7, a closed or partially closed bottom wall 9, and an approximately flat top wall 11 in which a circular or oval ion emitting slit and/or aperture (also sometimes referred to as a “discharge gap”) 15 is defined. The bottom wall 9 and side wall 7 of the cathode 5 are optional. Ion emitting slit/aperture 15 includes an inner periphery as well as an outer periphery. The portion of top cathode wall 5, 11 inside of the slit 15 is considered the inner cathode, whereas the portion of the top cathode wall 5, 11 outside of the slit 15 is considered the outer cathode. Deposit and/or maintenance gas supply aperture or hole(s) 21 is/are formed in bottom wall 9. Flat top wall 11 of the cathode functions as an accelerating electrode. A magnetic system including a cylindrical magnet 23 with poles N and S of opposite polarity is placed inside the housing between bottom wall 9 and top wall 11. The N-pole faces flat top wall 11, while the S-pole faces bottom wall 9. The purpose of the magnetic system with a closed magnetic circuit formed by the magnet 23 and cathode 5 is to induce a substantially transverse magnetic field (MF) in an area proximate to ion emitting slit 15.
The ion source may be entirely or partially within conductive wall 50, and/or wall 50 may at least partially define the deposition chamber. In certain instances, wall 50 may entirely surround the source and substrate 45, while in other instances the wall 50 may only partially surround the ion source and/or substrate.
A circular or oval shaped conductive anode 25, electrically connected to the positive pole of electric power source 29, is arranged so as to at least partially surround magnet 23 and be approximately concentric therewith. Anode 25 may be fixed inside the housing by way of insulative ring 31 (e.g., of ceramic). Anode 25 defines a central opening therein in which magnet 23 is located. The negative pole of electric power source 29 is grounded and connected to cathode 5, so that the cathode is negative with respect to the anode. Generally speaking, the anode 25 is generally biased positive by several thousand volts. Meanwhile, the cathode (the term “cathode” as used herein includes the inner and/or outer portions thereof) is generally held at ground potential. One example of a conventional ion source includes an anode having a flat top surface approximately 2 mm from the bottom of both the inner and outer cathodes.
The conventional ion beam source of FIGS. 1-3 is intended for the formation of a unilaterally directed tubular ion beam, flowing in the direction toward substrate 45. Substrate 45 may or may not be biased in different instances. The ion beam emitted from the area of slit/aperture 15 is in the form of a circle in the FIG. 2 embodiment and in the form of an oval (e.g., race-track) in the FIG. 3 embodiment. The conventional ion beam source of FIGS. 1-3 operates as follows in a depositing mode when it is desired that the ion beam deposit at least one layer on substrate 45. A vacuum chamber in which the substrate 45 and slit/aperture 15 are located is evacuated, and a depositing gas (e.g., a hydrocarbon gas such as acetylene, or the like) is fed into the interior of the source via aperture(s) 21 or in any other suitable manner. A maintenance gas (e.g., argon) may also be fed into the source in certain instances, along with or instead of the depositing gas. Power supply 29 is activated and an electric field is generated between anode 25 and cathode 5, which accelerates electrons to high energy. Anode 25 is positively biased by several thousand volts, and cathode 5 is at ground potential as shown in FIG. 1. Electron collisions with the gas in, and/or proximate to, aperture/slit 15 leads to ionization and a plasma is generated. “Plasma” herein means a cloud of gas including ions of a material to be accelerated toward substrate 45. The plasma expands and fills (or at least partially fills) a region including slit/aperture 15. An electric field is produced in slit 15, oriented in the direction substantially perpendicular to the transverse magnetic field, which causes the ions to propagate toward substrate 45. Electrons in the ion acceleration space in and/or proximate to slit/aperture 15 are propelled by the known E×B drift in a closed loop path within the region of crossed electric and magnetic field lines proximate to slit/aperture 15. These circulating electrons contribute to ionization of the gas (the term “gas” as used herein means at least one gas), so that the zone of ionizing collisions extends beyond the electrical gap between the anode and cathode and includes the region proximate to slit/aperture 15 on one and/or both sides of the cathode 5. For purposes of example, consider the situation where a silane and/or acetylene (C2H2) depositing gas is/are utilized by the ion source of FIGS. 1-3 in a depositing mode. The silane and/or acetylene depositing gas passes through the gap between anode 25 and cathode 5.
Unfortunately, the ion source of FIGS. 1-3 suffers several drawbacks. For example, conventional ion sources have small zones in which the ions can accelerate, thus limiting the overall energy efficiency of the ion source. Lower energy efficiencies may decrease the associated ion energies, which is not desirable in certain instances. The ions may tend to drift, potentially resulting in a less focused or otherwise less efficient ion beam. Also, the depth to which ions can penetrate the target substrate, if desired, may be limited by a lower ion energy.
Thus, it will be appreciated that there exists a need in the art for an ion source that overcomes one or more of the aforesaid problems.
In certain example embodiments, an ion source capable of emitting an ion beam is provided. Such an ion source may comprise an anode and a cathode, with the anode and/or the cathode having a discharge gap (e.g., slit or the like) formed therein. At least one magnet capable of generating a magnetic field proximate to the discharge gap also may be provided. A power supply may be in electrical communication with the anode and/or the cathode. The anode and/or the cathode may have a recess formed therein in which ions to be included in the ion beam can accelerate, the recess having a base and at least first and second sidewalls which may extend upwardly from the base toward the discharge gap and/or toward the other of the anode or cathode. The ion beam may be emitted from an area in and/or proximate to the discharge gap.
According to certain example embodiments of this invention, the recess may optionally be in communication with one or more optional gas-flow holes or channels (the gas-flow holes or channels also being defined in the electrode in which the recess is defined) through which gas is capable of flowing. According to certain example embodiments, the one or more optional gas-flow holes or channels may be tapered such that the holes or channels narrow toward the recess.
In certain example embodiments of this invention, there is provided a ion source capable of emitting an ion beam, comprising: a cathode including a discharge gap defined therein; an anode located at least partially below the discharge gap; at least one magnet capable of generating a magnetic field proximate to the discharge gap; a power supply in electrical communication with the anode and/or the cathode; and a recess defined in a top surface of the anode, the recess having a base wall and sidewalls and being located at least partially below the discharge gap.
In other example embodiments of this invention, there is provided an ion source capable of emitting an ion beam, comprising: an anode and a cathode, one of the anode and cathode having a discharge gap defined therein and the other of the anode and cathode having a recess defined therein in a location proximate the discharge gap, the recess having a base wall and at least one sidewall; at least one magnet capable of generating a magnetic field proximate to the discharge gap; and a power supply in electrical communication with the anode and/or the cathode.
In still further example embodiments of this invention, there is provided a method of operating an ion source capable of emitting an ion beam, the method comprising: providing an ion source including an anode and a cathode, the anode and/or the cathode having a discharge gap formed therein, and the anode and/or the cathode being in electrical communication with a power supply; using at least one magnet to generate a magnetic field proximate to the discharge gap; and accelerating ions to be included in the ion beam in and/or proximate to a recess formed in the anode and/or the cathode, the recess including a base wall and at least one side wall.
According to certain example embodiments, the ion beam may be used for cleaning the substrate, activation, polishing the substrate, etching the substrate, and/or depositing thin-film coating(s)/layer(s) on the substrate.